Washington: Exactly a year before the presidential polls, half of Americans say President Barack Obama does not deserve to be re-elected versus 40 percent who say he does, according to a new poll.

Independents, in particular, have lost faith in the Democratic president, says the Christian Science Monitor/TIPP poll released Monday. But attitudes can change a lot in a year, as history shows, it says.

Moreover, Obama's performance scores as many failing grades as it does soaring marks from the general public, it said.

Thirty-five percent of independents, the critical mass of voters with the power to swing presidential elections, say Obama deserves to be re-elected, while 56 percent believe he does not, according to the poll. Ten percent are not sure or did not say.

Among Americans of all political persuasions, 40 percent of those polled would give Obama four more years, 50 percent would not, 6 percent were not sure, and 4 percent declined to answer.

"The independent support is key. They are a key voting bloc to get him reelected," says Raghavan Mayur, president of TechnoMetrica Market Intelligence, which conducted the poll of 901 Americans. "When your support is weak among independents, it really is concerning."

If history is any guide, however, Obama's current approval ratings will be an unreliable predictor of his fate in the November 2012 contest, the Monitor said.

With the Republican nomination race in full swing and early-state primary elections just two months away, the Republicans' lack of consensus around or enthusiasm for a particular candidate could play in Obama's favour, it said.

"Obama should indeed be worried, but so should the Republicans," H.W. Brands, a professor of history at the University of Texas at Austin, was quoted as saying.

Gallup's historical data indicate that Obama's approval ratings, while grim, are not without precedent for re-election.

In the 10th quarter of his presidency (between April 20 and July 19, 2011), Obama's job approval average, at 46.8 percent, was sub-50 percent, the threshold that pundits and journalists use to gauge a leader's appeal in the run-up to an election.

But Bill Clinton and Ronald Reagan also rated below that marker during the same period of their respective first terms. Clinton was at 49.3 percent, and Reagan scored a meagre 44.4 percent. Both, of course, went on to a re-election.